Various nitrogen surface-treatments (e.g., nitriding, carbonitriding, nitrocarburizing, etc.) are known as surface hardening processes. These processes can involve diffusing varying levels of nitrogen into a variety of ferrous alloys (e.g., steels) to form nitrogen-rich surfaces. The diffused nitrogen can react with alloys of steel to enhance surface hardness. Nitrogen surface-treatments may result in a component that has a high surface hardness and a softer core. Nitrogen surface-treatments, therefore, may be useful for treating high wear components such as gears and shafts. Additionally, nitrogen surface-treatments may improve the fatigue life and the corrosion resistance of a component.
In most nitrogen surface-treatment processes, for example, the depth of diffusion of nitrogen into the steel may be controlled by the temperature of the component and the time of exposure to a gaseous environment containing nitrogen. Most often, a part to be treated is heated in a furnace to a desired temperature in an environment including nitrogen. One significant advantage of certain nitrogen surface-treatments, including nitriding, is that the case hardness may be developed without quenching.
While known nitrogen surface-treatment methods may achieve acceptable surface hardness levels, these methods include several disadvantages. For example, a part may be treated in an atmospheric nitrogen-treatment oven. In such ovens, however, small or thin features of the part will generally heat faster than the remainder of the surface of the part. As a result, these features may exhibit a higher hardness than the rest of the part. Moreover, atmospheric ovens are generally slow and lack the ability to precisely control the temperature of the part.
Nitrogen surface-treatments may also be performed in a vacuum furnace. In this arrangement, the part may be placed in a vacuum chamber, which is then evacuated. The part is heated to a desired temperature and nitrogen, and optionally other gases, may be supplied to the vacuum chamber. While this method may produce surfaces with uniform hardness values, it can be costly and time-consuming to establish and maintain the required vacuum during the surface-treatment.
Nitrogen surface-treatments, including nitriding, for example, have also been performed by exposing the part to a plasma containing nitrogen. While plasma nitriding methods may offer potential increases in heating rates over traditional furnace nitriding methods, these plasma-assisted methods normally involve the use of costly vacuum equipment to establish the necessary vacuum environments.
The present invention solves one or more of the problems associated with known nitrogen surface-treatments.